I'll just copy Warschauer's list of the reasons computers can have a positive influence on motivation:
“(a) the novelty of working with a new medium (Fox, 1988),
(b) the individualized nature of computer-assisted instruction (Relan, 1992),
(c) the opportunities for learner control (Hicken, et al., 1992; Kinzie, et al.,
1988; Pollock and Sullivan, 1990; Williams, 1993), and
(d) the opportunities for rapid, frequent non-judgmental feedback (Armour-Thomas,
et al., 1987; Waldrop, 1984; Wu, 1992).” (all cited in Warschauer 1996)